Controllers for electric motors are typically large, bulky devices. The industry standard is to mount the controller apart from the motor.
In certain environments, the separation of the controller from the motor leads to several undesirable consequences. For instance, in environments in which high RF fields are present, the conductors connecting the motor to the controller act as antennae that pick up the RF signals. As a result, these conductors must be shielded against this electromagnetic interference. In environments such as outer space, the conductors are subject to inductive heating. Because heat cannot be dissipated into a vacuum, the conductors and connectors burn. Therefore, heat sinks must be provided to dissipate the heat from the conductors and connectors.
In certain applications, the bulkiness of the controller and the above-mentioned problems make it impractical to use. For instance, a controller is impractical to use in a Portable Life Support System (PLSS) for an EVA suit. Among its many functions, the PLSS provides an astronaut with an oxygen/nitrogen atmosphere in which to breathe. As the astronaut exhales, he expels carbon dioxide into his helmet. To maintain the oxygen/nitrogen atmosphere, the PLSS removes carbon dioxide from the helmet through a closed loop ventilation. A motor-driven fan circulates the carbon dioxide within the ventilation loop. To avoid using a controller for the fan, the motor is operated at a fixed speed.
Yet, by fixing motor speed, other problems arise. During a space mission, gas pressure can vary from 19.5 psia down to 6 psia, a variation of better than 3:1. As the pressure is doubled, for example, the mass flow is also doubled. Because the speed of the motor is fixed, the increase in pressure causes a mass flow that is greater than necessary. Thus, higher pressures cause a significant energy drain on the battery pack. Higher pressures can also result in ventilation mass flow rates that are higher than desired.
Therefore, it is an object of the present invention to provide a motor with an integral controller.
It is a further object of the present invention to provide an integral controller that operates a brushless motor at constant torque and variable speeds for use in a circulation loop under variable pressure.